The proposed work focuses on alginate, an exopolysaccharide which functions as a major virulence factor in Pseudomonas aeruginosa strains which colonize the lungs of cystic fibrosis patients. Alginate is also produced by the phytopathogen Pseudomonas syringae and is presumed to contribute to both virulence and symptom development. The biosynthesis of alginate by P. aeruginosa and P. syringae presents us with a unique opportunity to study a virulence factor which functions in bacteria which are pathogenic to both humans and plants. The long-term objective of this project is to identify sequence motifs, regulatory cascades, or environmental signals which differentiate alginate production in P. aeruginosa and P. syringae, thus providing insight into the adaptation of pathogens to human and plant hosts, respectively. In the proposed work, the regulation of the algD promoter in P. aeruginosa and P. syringae will be compared (algD encodes GDP-mannose dehydrogenase, a highly regulated enzymatic step in alginate biosynthesis). The role of copper, a transcriptional signal for algD induction in P. syringae but not in P. aeruginosa will be investigated. The potential functions of AlgR and AlgT, key regulatory proteins of alginate biosynthesis in P. aeruginosa, will be examined in P. syringae. A genetic approach will be utilized to investigate the contribution of alginate to the virulence and fitness of several P. syringae strains. Plasmid-encoded genes which confer constitutive production of alginate to P. syringae will be characterized.